I have a detached single car garage. I will soon be turning it into a small woodshop / workshop.
Right now there is a 20 amp line run out to the garage. I would like to install a Sub-Panel. Would there be any problems installing a 100 amp breaker into a existing 100amp service panel to supply the sub-panel?
My biggest draw at the moment is a 13" Thickness planer. Other than that is small bench power tools. And none of those would be run at the same time.
Thanks
Bill
None.
Just remember to use #1 (?) cable to take the amperage and voltage.
I think the number is right. The cable is about 1" thick. Both your main and your sub will have 100 amp breakers giving you a bit of insurance should anything go wrong and you will get a bonus in that you can back feed power from a generator by merely shutting off the main breaker. The bonus isn't quite what OSHA would want, but it works.
Bill Davis Jr wrote in news: snipped-for-privacy@4ax.com:
Some panels have a limit to how much power they can deliver over a single bus connection. That should be documented on the sticker in the panel. That and space in the panel for wires that big would probably be your main technical issues.
Practically I'm not sure why you want to do this. 100a breakers are typically several times more expensive than 60a and under. If you actually were drawing 100a in the garage then you couldn't have anything else on in the house at the same time. It also sounds like your simultaneous loads wouldn't come close to using that much anytime soon.
It may be smart to install 100a capable wiring if possible, especially if you're going underground. That way you could get there more easily in the future if you need it and do a service upgrade.
Doug
I think so, but I'm not an electrician. Sounds too big unless you have 200A service to the house.
Ask on rec.woodworking. A lot of guys there have shops and subpanels and can give you accurate information. Be sure to allow for the 3hp saw down the road that needs 220V. Ideal would be 220 lines for the tablesaw, dust collector, maybe the jointer if you get a big one.
#1 is more than NEC calls for. If you have a 200amp panel in the house and want to run a 100amp sub panel, you will need to run #2AL or #4 Copper. You will find that the Aluminum is much cheaper. I am doing the same thing. All I really needed was 60amp service to the garage, but it turns out cheaper to run a 100amp service based on wiring costs/availability. #6 copper is way more expensive than #2 AL. You will also need a grounding rod most likely. You should contact the inspector to see if there is anything specific required in your area.
Ummmm.... this depends a LOT on the specifics of the installation. 100 amps on #4 copper single insulated conductors in free air is OK, but NOT in raceway or cable or earth. Ditto #2 aluminum, with the additional caveat that it *also* depends on the temperature rating of the conductor insulation, e.g. #2 aluminum UF cable is limited to 75A, but #2 aluminum THHN is OK at 100A.
garage,
area.
Normally the wire size you specify applies to service entrance conductors...
Doug I'm not trying to quibble when I say that the 90 degree column is useful only when derating the wire do to the number of conductors in a cable or raceway or the ambient temperature. Very few terminals are actually rated at 90 degrees centigrade so your final ampacity is limited to the ampacity of the conductor at the temperature rating of the terminals to which it is connected. Since the ampacity of the #2 Al is ninety amperes at 75 degree centigrade rating of most terminals and that is a standard breaker and fuse size a larger wire is required.
WOW!
I brought this up to a fellow electrician. Why are we allowed to use #2 AL for 100amp subpanel, and he said he's used #2 for servers and feeders for dwellings for years, per Table 310.15(B)(6). I agreed, and said I wasn't feeding a dewlling, just a sub panel in the same dwelling, so per 110.14(c)(1) and table 310.16 and limited by 75C terminals on the sub panel and feeder breaker aren't I limited to 90 amps?
The concensious is #2 AL is good for 100 amps because of Table
310.15(B)(6) reguardless if it's feeding a dewelling or a portion of a dewelling, it's still a dewelling (loads).Can anyone confirm this?
later,
tom
installation. 100 amps on
actually
terminals to
310-15(b)(6)120/240 volt, 3 wire, single phase dwelling service and feeders
For dwelling units, conductors as listed in Table 310-15(b)(6) shall be permitted as 120/240 volt 3 wire single phase service entrance conductors, service lateral conductors, and feeder conductors that serve as the main power feeder to a dwelling unit and are installed in raceway or cable with or without an equipment grounding conductor. For application of this section, the main power feeder shall be the feeder(s) between the main disconnect and the lighting and appliance branch circuit panelboards...
The last line is kind of vague, does a subpanel qualify? I've always considered Table 310-15(b)(6) as just for service drops...
agreed,
conductor.
OK, I looked at an older (1990) version of an NEC handbook. A footnote in the handbook states in part "If there are panelboards on the load side of the main service-entrance equipment supplied by feeders, Note
3 also permits a reduction in the conductor size of these feeders as a result of a revision for the 1990 NEC".Can't say if that's still in effect for 2005...
installed
appliance
footnote
The two illustrations of an allowed reduction in conductor size in the
1990 Handbook has are of a common service for three apartments. 1 Each connected to a meter and a service disconnecting means at the panelboards-still considered a service drop from the meters to the panelboard 2 Each having a service disconnect at the meter instead of the panelboard-considered a feeder between the disconnect and the panelboard.
Once you are supplying a part of the dwellings load you are no longer sizing the "the main power feeder to a dwelling unit." The is a singular pronoun. Subpanel supply feeders simply cannot be the main power feeder to the dwelling unit.
(6) 120/240-Volt, 3-Wire, Single-Phase Dwelling Services and Feeders. For dwelling units, conductors, as listed in Table 310.15(B)(6), shall be permitted as 120/240-volt, 3-wire, single-phase service-entrance conductors, service lateral conductors, and feeder conductors that serve as the main power feeder to a dwelling unit and are installed in raceway or cable with or without an equipment grounding conductor. For application of this section, the main power feeder shall be the feeder(s) between the main disconnect and the lighting and appliance branch-circuit panelboard(s).
OK, fine -- doesn't change the fact that the previous poster was undersizing the job.
I agree. I just didn't want to leave anyone with the impression that a ninety degree column ampacity would ever be the ending point for an ampacity question.
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